1. Field of the Invention
The present invention relates to an ink composition for ink jet recording which can offer high print quality and highly reliable images on plain papers, recycled papers, and specialty recording media for ink jet recording, and an ink jet recording method which can realize such images.
2. Background Art
Ink jet recording is a method wherein an ink is ejected as droplets through fine nozzles to record letters or figures onto the surface of recording media. Ink jet recording systems which have been developed and put to practical use include: a method wherein an electric signal is converted to a mechanical signal using an electrostrictive element to intermittently eject an ink reservoired in a nozzle head section, thereby recording letters or symbols on the surface of a recording medium; and a method wherein an ink, reservoired in a nozzle head section, in its portion very close to the ejection portion is rapidly heated to create a bubble and the ink is intermittently ejected by volume expansion created by the bubble to record letters or symbols on the surface of a recording medium.
Various properties required of inks used in the above ink jet recording are such that the drying property of the print is good, no feathering is created in prints, uniform printing can be realized on the surface of all the recording media, and, in the case of multi-color printing, color-to-color intermixing does not occur. In particular, what is important for ink used in printing on paper as the recording medium is to effectively prevent feathering or bleeding attributable to a difference in wettability of the surface of paper by ink, especially bleeding at the boundary areas between contiguously printed black ink and color ink, and to improve the quality of printed images through an improvement in color development and fixation of a colorant on the recording medium. Among others, realization of good images has been desired for specialty recording media for ink jet recording which, in production thereof, have been optimized to be used in ink jet recording, as well as for plain papers which are inexpensive and easily available.
Various inks for ink jet recording, using a dye as a colorant have hitherto been proposed as inks which can yield good images on recording papers. For example, U.S. Pat. No. 5,183,502 proposes the addition of Surfynol 465 (manufactured by Air Products and Chemicals Inc., U.S.A.) as an acetylene glycol surfactant to dye-based inks, and U.S. Pat. No. 5,196,056 discloses the addition of both diethylene glycol mono-n-butyl ether and Surfynol 465 to dye-based inks.
Further, in order to realize images having good quality on plain papers, for example, Japanese Patent Laid-Open No. 41171/1991 proposes the use of a black ink, which is less likely to penetrate the recording medium, in combination with a color ink which is likely to penetrate the recording medium. Likewise, in order to realize images having good quality on plain papers, Japanese Patent Laid-Open No. 128514/1994 proposes a recording method wherein the deposition of a first liquid, containing a water-soluble resin having in its molecule at least one carboxyl group or anhydride thereof or sulfonic acid group, on a recording medium is followed by the deposition of a dye-containing ink on the recording medium in its liquid-deposited portion. Further, a variety of ink compositions using a pigment as a colorant have also been proposed. In most of these proposals, suppression of wetting of the surface of paper by ink by lowering the penetration of ink has been studied to improve the print quality, and this method has been put to practical use.
In many cases, however, conventional pigment-based inks have unsatisfactory penetration into paper. Therefore, even with the method wherein the wetting of the paper in its surface is suppressed, feathering or bleeding may be caused on plain papers, particularly on recycled papers. For this reason, a lot of time has been required for drying printed papers, and this has made it difficult to continuously perform printing. In particular, a recycled paper is an aggregate comprising components of various papers, and, hence, the components are different from each other or one another in ink penetration speed. This difference in ink penetration speed is likely to cause feathering or bleeding in prints.
Further, when pigment-based ink is printed, for example, on paper containing a conventional sizing agent, the pigment is often left on the surface of the paper or the like, leading to poor rubbing/scratch resistance of printed images, unless a certain level of ability to penetrate the recording media is imparted to this ink.
For the above reason, the development of a pigment-containing ink, which has excellent ability to penetrate recording media, can yield images having excellent rubbing/scratch resistance, can realize continuous and high-speed printing, and can provide prints having good image quality, has been desired in the art.
The present inventors have now found that an ink composition for ink jet recording can be provided which has an excellent ability to penetrate recording media, can realize continuous and high-speed printing, can offer high print density on plain papers and recycled papers, can realize high print quality free from feathering or bleeding, and has highly reliable printing performance. The present invention has been made based on such finding.
Accordingly, it is an object of the present invention to provide an ink composition for ink jet recording which has an excellent ability to penetrate recording media, can realize continuous and high-speed printing, and can produce prints having excellent quality.
Thus, according to one aspect of the present invention, there is provided an ink composition for ink jet recording, comprising at least a pigment, a 1,2-alkanediol, glycerin, a polyhydric alcohol derivative and/or an acetylene glycol surfactant, a water-soluble organic solvent, and water,
said pigment having been surface treated to render the pigment dispersible and/or dissolvable in water without any dispersant,
said 1,2-alkanediol being at least one member selected from the group consisting of 1,2-butanediol, 1,2-pentanediol, and 1,2-hexanediol,
said ink composition having a surface tension of not more than 40 mNmxe2x88x921  at 20xc2x0 C.
According to another aspect of the present invention, there is provided an ink jet recording method.
The ink jet recording method comprises the steps of: ejecting droplets of an ink composition; and depositing the droplets onto a recording medium to perform printing,
wherein printing is performed using an ink composition containing a pigment as a colorant and
an ink composition containing a dye as a colorant.
According to a further aspect of the present invention, there is provided an ink jet recording apparatus for practicing the above ink jet recording method.
The ink jet recording apparatus comprises:
recording medium-carrying means for holding and carrying a recording medium;
means for depositing, on the recording medium, an ink composition containing a pigment as a colorant and an ink composition containing a dye as a colorant to record an image; and
ink jet recording means for controlling the means for depositing the ink compositions to record an image.